33 ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , R IO DE JANEIRO 2013
T HE A STROPARTICLE P HYSICS C ONFERENCESwinson Flow and the Tilt Angle of the Neutral Current Sheet

H.KOJIMA1 , S.S HIBATA2 , A.O SHIMA2 , Y.H AYASHI3 , H.A NTIA4 , S.D UGAD4 , T.F UJII3 , S.K.G UPTA4 ,S.K AWAKAMI3 , M.M INAMINO3 , P.K.M OHANTY4 , I.M ORISHITA5 , T.NAKAMURA6 , T.N ONAKA7 , S.O GIO3 ,H.TAKAMARU2 , H.TANAKA3 , K.TANAKA8 , N.I TO3 , A.JAIN4 , T.M ATSUYAMA3 , B.R AO4 , K.YAMAZAKI3 ,N.YOSHIDA2 FOR THE ICRC C OLLABORATION .
1 Ai hi Institute of Te hnology
2 Chubu University
3 Osaka City University
4 Tata Institute of Fundamental Resear h
5 Asahi University
6 Ko hi University
8 Hiroshima City University
7 University of Tokyo
shibatais . hubu.a .jp
Abstra t: As theonsequen e of the Lorentz for e and the positive radial density gradient of osmi rays inthe heliosphere, when the interplanetary magneti eld (IMF) near the earth is dire ted toward the sun, the owof osmi rays perpendi ular to the e lipti plane from the north is indu ed and vi e versa. This IMF polarity
dependent ow is alled Swinson ow after the name of the rst proposer of the me hanism. We have investigated
the relationships between the Swinson ow and the tilt angle of the neutral urrent sheet at the solar sour esurfa e.

Keywords:

1

Swinson Flow, Interplanetary Magneti Field, Neutral Current Sheet, Tilt Angle.

Introdu tion

One of the important ows of osmi rays in the innersolar system, whi h is perpendi ular to both interplanetarymagneti eld (IMF) and radial density gradient, is alled
Swinson ow. To investigate the genuine sidereal daily
variations in gala ti osmi rays, one has to remove any
effe ts being aused by other reasons. The Swinson ow isthought to be one of su h auses and it would be the maineffe t on the sidereal daily variations.
The relationship between the sidereal variation of gala ti osmi rays whi h ould be aused by the Swinson ow
and the urrent sheet of the interplanetary magneti eldhas been analyzed. The distan e between the urrent sheet
and the earth is thought to affe t on Swinson ow strongly.
The urrent sheet is formed by the intrinsi boundary stru ture of the dipole magneti eld that would be pulling out
by the solar wind from the surfa e of the sun. The boundary between positive polarity and negative polarity of thesolar surfa e magneti eld in lines against the solar equator. Typi ally this slope, whi h is alled tilt angle, is not
so small that the urrent sheet forms a spiral wave up tothe end of the heliosphere. The amplitude of this wave anbe determined by the Tilt angle, and it an settle the earth
with the typi al distan e from the urrent sheet. In this paper, we analyze a relationship between Swinson ow andTilt angle with the data of the GRAPES-3 muon teles ope.
It is known that typi ally the Swinson ow an o urwhen Larmor radius of the osmi rays be ome longer
than the distan e between the urrent sheet and the earth.
However, su h a ondition an not exist regularly. As in theFig.1, Fig2, Fig3, there an be the ase that the Swinson
ow never o urs when the earth is on the urrent sheet.
This is be ause that a longer distan e between the urrent
sheet and the earth an't be yielded if the tilt angle is small.

: An isotropy due to the swinson ow is learly visi-Fig. 1

ble.

: An isotropy due to the swinson ow is not observ-Fig. 2

able.

Swinson Flow

33

ND I NTERNATIONAL C OSMIC R AY C ONFERENCE , R IO DE JANEIRO 2013

: An isotropy with the inverse phase an be observed.

:Fig. 3Fig. 6:

Fig. 7: Computed tilt angle in the period of this analysis.

Fig. 4

nent of mixed ows was vanished well and the phase of ananisotropy with expe ted shape has been obtained. However the amplitude of it is be oming small, possibly. Beause the phases of opposite ould not be vanished in theanalysis (T+A)/2, we have to adopt any step to investigate
the genuine sidereal daily variation.
A knowledgment:This work is supported by the grants-inaid of the Solar-Terrestrial Environment Laboratory of Nagoya
University and the Institute for Cosmi Ray Resear h of University of Tokyo.

Referen es:Fig. 52Analysis

The variation of the tilt angle omputed by the Wil oxsolar observatory in the period of this analysis is shownin Fig.4. The period has been divided into three periods
whi h have been labeled as A, B and C, respe tively.

3Summary

The tilt angle whi h is related to an amplitude of the urrent sheet wave have a variation in time. As from the analysis at both the region of Toward and Away, the relationship between the tilt angle and the Swinson Flow implies that there is a mixture of different ows whi h havea reverse polarity vi e versa. In the analysis of (T-A)/2,
where the Away was subtra ted from Toward, a ompo-[1℄ Swinson, D. B., Siderial osmi -ray variation, Jour.
Geophys. Res., 74 (1969) 5591-5598[2℄ Duldig, M. L., Australian osmi ray modulation resear h,
Publi ations of the Astronomial So iety of Australia, 18.2
(2001) 12-40[3℄ Yasue, S., North-South Anisotropy and Radial Density
Gradient of Gala ti Cosmi Rays, Jour. Geomag. Geoele.,
32 (1980) 617-635[4℄ http://wso.stanford.edu/Tilts.html